Many transmembrane proteins are proteolytically released from the cell surface by a process known as ectodomain shedding. Shedding occurs under normal physiologic conditions and can be increased in certain pathologies. Among the many receptors for which ectodomain shedding has been demonstrated is c-Met, the hepatocyte growth factor (“HGF”) receptor tyrosine kinase (Komada et al., FEBS Lett 1993; 328:25-9, Wajih et al., Circ Res 2002; 90:46-52). HGF is a pleiotropic heparin-binding protein identified and isolated based on observations of its mitogenic activity on hepatocytes and epithelial cells, and independently identified and isolated based on observations of its ability to stimulate cell motility (scatter factor or SF). (Comoglio et al., Semin Cancer Biol 2001; 11:153-65, Funakoshi et al., Clin Chim Acta 2003; 327:1-23). HGF is typically produced by cells of mesenchymal origin and acts in a paracrine manner on a variety of cellular targets including epithelial and endothelial cells, hematopoietic cells, neurons and melanocytes during embryonic development and throughout adulthood, in normal and pathological processes (Birchmeier et al., Nat Rev Mol Cell Biol 2003; 4:915-25). HGF is essential for embryonic development, where it is involved in somite migration, limb bud and limb skeletal muscle formation, placenta formation (Schmidt et al., Nature 1995; 373:699-702, Uehara et al., Nature 1995:373:702-5) and later in organogenesis (Rosario et al., Trends Cell Biol 2003; 13:328-35), in neural development (Birchmeier et al., Trends Cell Biol 1998:8:404-10) and in tissue repair and regeneration (Jin et al., J Pharmacol Exp Ther 2003; 304:654-60, Huh et al., Proc Natl Acad Sci USA 2004; 101:4477-82). While the role of HGF in adult homeostasis is not yet completely understood, a growing body of evidence suggests that it is an endogenous tissue protective factor for several major organs and has potent antifibrotic activity (Liu, Am J Physiol Renal Physiol 2004; 287:F7-16).
The MET oncogene was isolated from a human osteogenic sarcoma cell line that had been chemically mutagenized in vitro. Transforming activity was due to a DNA rearrangement where sequences from the TPR (translocated promoter region) locus on chromosome 1 fused to sequences from the MET locus on chromosome 7 (TPR-MET) (Furge et al., Oncogene 2000; 19:5582-9). This rearrangement has been found in patients with gastric carcinoma (Yu et al., Cancer 2000; 88:1801-6). Isolation of the full-length MET proto-oncogene coding sequence revealed structural features of a membrane spanning receptor tyrosine kinase (Furge et al., Oncogene 2000; 19:5582-9). The identification of HGF as the natural ligand for c-Met and the identity of SF and HGF united a collection of findings demonstrating that a single receptor transduced multiple biological activities including motility, proliferation, survival and branching morphogenesis (Birchmeier et al., Nat Rev Mol Cell Biol 2003; 4:915-25). Activation of the c-Met intrinsic tyrosine kinase (TK) activity was required for all of these activities. Consistent with its relationship with HGF, c-Met is widely expressed early in development, deletion of the gene is embryonic lethal in mice, and widespread expression persists throughout adulthood (Birchmeier et al., id). Both HGF and c-Met are upregulated after kidney, liver or heart injury, suggestive of a general mechanism of protection against tissue damage, as well as one of tissue repair and regeneration (Matsumoto et al., Kidney Int 2001; 59:2023-38, Michalopoulos et al., Science 1997; 276:60-6, Nakamura et al., J Clin Invest 2000; 106:1511-9).
HGF and c-Met are implicated in a wide variety of human malignancies including colon, gastric, bladder, breast, kidney, liver, lung, head and neck, thyroid and prostate, but also sarcomas, hematological malignancies, melanoma and central nervous system (CNS) tumors (Birchmeier et al., Nat Rev Mol Cell Biol 2003; 4:915-25, Birchmeier et al., Ciba Found Symp 1997; 212:230-40). Through paracrine signaling, overexpression of ligand and/or receptor, autocrine loop formation and/or receptor mutation and gene rearrangement, this signaling pathway can enhance tumor cell growth, proliferation, survival, motility and invasion. Inappropriate c-Met signaling in disease can resemble, at least in part, developmental transitions between epithelial and mesenchymal cell types normally regulated by HGF. Among the many genes upregulated in response to activation of this pathway is that of the receptor itself, creating the potential for c-Met overexpression in otherwise normal target cells through persistent ligand stimulation; consistent with this, c-Met overexpression is widely observed in cancers of epithelial origin where paracrine delivery of HGF results in dysregulated signaling, whereas cells of mesenchymal origin that normally express HGF often acquire c-Met expression, and several sarcomas display autocrine c-Met signaling (Furge et al., Oncogene 2000; 19:5582-9). Importantly, the c-Met pathway activates a program of cell dissociation and increased cell motility coupled with increased protease production that has been shown to promote cellular invasion through extracellular matrices, and that closely resembles tumor metastasis in vivo (Birchmeier et al., Ciba Found Symp 71 p 1997; 212:230-40). In addition, pathway activation in vascular cells stimulates tumor angiogenesis, facilitating tumor growth for cancers that are growth limited by hypoxia, and promoting tumor metastasis. Hypoxia alone upregulates c-Met expression and enhances HGF/SF signaling in cultured cells and mouse tumor models (Pennacchietti et al., Cancer Cell 2003; 3:347-61).
Early diagnosis is a key strategy in cancer treatment. Although it is known that c-Met is overexpressed in certain cancers, a need exists for a screening test for c-Met that is sensitive, cost-efficient, and can be used for diagnosis, determining stage of disease, prognosis, and/or assessing the efficacy of therapeutic intervention. The invention is directed to this and other ends.